In integrated circuit manufacturing, microelectronic devices such as capacitors are the basic energy storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and ferroelectric memory (FERAM) devices. Capacitors typically consist of two conductors acting as electrodes, such as parallel metal (e.g., platinum) or polysilicon plates, that are insulated from each other by a layer of dielectric material.
Historically, silicon dioxide has generally been the dielectric material of choice for capacitors. However, the continuous shrinkage of microelectronic devices over the years has led to dielectric layers approaching only 10 Å in thickness (corresponding to 4 or 5 molecules). To reduce current tunneling through thin dielectric layers, high dielectric metal-containing layers, such as Al2O3, TiO2, ZrO2. HfO2, Ta2O5, (Ba,Sr)TiO3. Pb(Zr,Ti)O3 and SrBi2Ti2O9, have been developed to replace SiO2 layers. However, these metal-containing layers can provide high leakage paths and channels for oxygen diffusion, especially during annealing. Also, an undesirable interfacial layer of SiO2 is frequently created by oxidation of polysilicon during the annealing of the dielectric layer.
One way to address these problems is to deposit a thin, conductive, amorphous, metal nitride barrier layer on the substrate prior to the deposition of the thin resistive metal oxide layer. For example, reactive metal silicon nitride barrier metal layers are used to protect polysilicon from oxygen diffusion prior to applying very thin (i.e., less than 10 Å) barium strontium titanate dielectric films.
Refractory metal nitrides and refractory metal silicon nitrides, such as titanium nitride (Ti—N), tantalum nitride (Ta—N), tungsten nitride (W—N), molybdenum nitride (Mo—N), titanium silicon nitride (Ti—Si—N), tantalum silicon nitride (Ta—Si—N) and tungsten silicon nitride (W—Si—N), are also useful as conductive barrier layers between silicon substrates and copper interconnects to reduce copper diffusion. This copper diffusion has led to degradation of device reliability, causing semiconductor manufacturers to turn toward other less conductive metals, such as aluminum and tungsten.
Further improvements in high temperature adhesion and diffusion resistance can be realized when about 4 to about 30 atom % silicon is incorporated to form a more amorphous metal silicon nitride layer. Examples of refractory metal silicon nitrides that are useful as barrier layers include tantalum silicon nitride (Ta—Si—N), titanium silicon nitride (Ti—Si—N), and tungsten silicon nitride (W—Si—N).
Methods for using physical vapor deposition (PVD) methods, such as reactive sputtering, to form Ta—Si—N barrier layers are known. Hara et al., “Barrier Properties for Oxygen Diffusion in a TaSiN Layer,” Jpn J. Appl.-Phys., 36(7B), L893 (1997) describe noncrystalline, low resistivity Ta—Si—N layers that acts as a barrier to oxygen diffusion during high temperature annealing at 650° C. in the presence of O2. The Ta—Si—N layers are formed by using radio-frequency reactive sputtering with pure Ta and Si targets on a 100 nm thick polysilicon layer. Layers having relatively low silicon content, such as Ta0.50Si0.16N0.34 are stated to have a desirable combination of good diffusion barrier resistance along with low sheet resistance. These Ta—Si—N barrier layers have improved peel resistance over Ta—N barrier layers during annealing conditions.
Lee et al., “Structural and chemical stability of Ta—Si—N thin film between Si and Cu,” Thin Solid Films, 320:141-146 (1998) describe amorphous, ultra-thin (i.e., less than 100 Å) tantalum-silicon-nitrogen barrier films between silicon and copper interconnection materials used in integrated circuits. These barrier films suppress the diffusion of copper into silicon, thus improving device reliability. Barrier films having compositions ranging from Ta0.43Si0.04N0.53 to Ta0.60Si0.11N0.29 were deposited on silicon by reactive sputtering from Ta and Si targets in an Ar/N2 discharge, followed by sputter-depositing copper films.
However, when PVD methods are used, the stoichiometric composition of the formed metal nitride and metal silicon nitride barrier layers such as Ta—N and Ta—Si—N can be non-uniform across the substrate surface due to different sputter yields of Ta, Si, and N. Due to the resulting poor layer conformality, defects such as pinholes often occur in such layers creating pathways to diffusion. As a result, the effectiveness of a physically deposited diffusion barrier layer is dependent on the layer being sufficiently thick.
Vapor deposition processes such as atomic layer deposition (ALD) processes are preferable to PVD processes in order to achieve the most efficient and uniform barrier layer coverage of substrate surfaces. There remains a need for an ALD process to form refractory metal nitrides (especially Ta—N layers) on substrates, such as semiconductor substrates or substrate assemblies.